This proposal is for a study of the role of proprioceptive and chemical inputs in determining neural output to the expiratory muscles of the chest and abdominal wall. The work, which is directed at an investigation of abnormalities in respiratory control in pulmonary disease employs control systems techniques in the design and analysis of physiological experiments. The primary aim of this work is to investigate the overall reflex loops relevant to expiration by recording from internal intercostal and abdominal expiratory nerves and examining the effects on these neurograms of controlled changes of the inputs which modify them: chemical drive, pulmonary vagal afferent activity and proprioceptive afferent activity from the chest and abdominal wall muscles. In preliminary experiments in anethetized dogs in which proprioceptive afferent activity from the chest and abdominal wall was minimized by paralysis with gallamine, I find that increased vagal stretch receptor activity inhibits the rate of rise of peripheral expiratory activity (as recently reported by Polacheck, Remmers and Younes (Fed. Proc. 37:806, 1978)). I propose to use an original vacuum pumping system, which I have designed to control the main vagal inputs during expiration, to carry out a detailed investigation of this feedback, loop, including an examination of whether it exhibits time dependence, how afferent inputs from chemoreceptors interact with the reflex loop, whether the effect of lung volume on peripheral expiratory activity depends solely on instantaneous lung volume or does expiratory airflow exert a separate influence, and an investigation of our hypothesized physiological function of this reflex loop. Further I plan to examine the effects on peripheral expiratory activity of the other proprioceptive afferent input which influences expiratory activity, proprioceptive afferent activity from the chest and abdominal wall, while holding vagal afferent and chemical inputs constant.